1. Field of the Invention
This invention relates to a vehicle electrical system that can provide a higher voltage from an alternator to a first group of power consumers in the vehicle and that can simultaneously provide a lower voltage from the alternator to a second group of power consumers in the vehicle.
2. Description of the Related Art
Traditionally, the electrical loads of an automobilexe2x80x94such as lighting systems, radio players, windshield wipers, horns, etc.xe2x80x94receive electrical power from an on-board electrical storage device such as a 12 volt (nominal) battery. The 12 volt battery is charged by an alternator operating at about 14 volts, and the voltage from the alternator and/or 12 volt battery is used as a standard electrical power input for the varied types of electrical loads placed on the automobile, including continuous loads, prolonged loads, and intermittent loads.
In recent years, the 12 volt vehicle battery and the 14 volt alternator have been called upon to supply increasingly greater electrical power to more and more electrical loads. Moreover, this demand will, no doubt, continue as new power consumers are continually added to vehicles. For example, electrically pre-heated catalytic converters, electrically power-assisted steering, and seat and windshield heaters are now commonplace, as are other power consumers. Hence, there is significant interest in replacing the 12 volt vehicle battery with a battery having a higher voltage, such a 36 volt (nominal) battery, which is coupled to an alternator having a charging voltage of about 42 volts.
While higher voltage batteries and alternators do provide increased electrical power, many traditional electrical components cannot handle increased voltages without overheating, burning out, or both. For instance, traditional headlights and tail lights would rapidly burn out if powered by a 36 volt battery and/or a 42 volt alternator; in other words, these electrical components would essentially become a fuse for such an electrical system. Therefore, in order to avoid the expense of redesigning many traditional electrical components to handle the increased voltages in a vehicle using a 42 volt alternator, a means for supplying a lower voltage from the 42 volt alternator is needed.
An alternator that is presently widely used for the charging of the battery in vehicles is a three phase alternator. The windings in the alternator are wound as a three phase Y-winding (also called star winding). The output of the alternator is rectified through a full wave rectifier to change the alternating current to direct current. A typical three-phase full-wave rectifier consists of paired uni-directional conducting devices, normally solid state diodes, connected in series. The diodes conduct in a single direction and by appropriate interconnection of the windings and the paired diodes, current flow is established from the three phase winding to a positive output line, through the battery and/or loads and a through return line connected to the opposite side of the three-phase windings.
Theoretically, the current flow in the Y-winding of the alternator should be so balanced and arranged that there is a zero potential and current available at the common center connection point (also called the neutral point) of the Y-connected windings. However in practice, a voltage potential develops at the common point. Typically, the common point provides an average voltage that is about one half of the full-wave rectified output voltage of the alternator. This voltage has been used and connected into prior art electrical systems for the operating of auxiliary loads, such as indicating lamps and the like. (See, for example, the dual voltage alternators of U.S. Pat. Nos. 4,816,736, 5,661,368, and 5,719,486.) Accordingly, it can be appreciated that these patents suggest one means for tapping a second lower voltage from an alternator in order to power electrical components having a lower voltage capacity.
However, if the alternators described in U.S. Pat. Nos. 4,816,736, 5,661,368 and 5,719,486 were to be reconfigured to output 42 volts as proposed above, these alternators would present problems in a typical vehicle electrical system. Specifically, the common point of a 42 volt Y-winding alternator would provide an average voltage of about 21 volts. This 21 volt average output would be above the voltage capacity of many traditional electrical components in a vehicle. Therefore, the alternators described in U.S. Pat. Nos. 4,816,736, 5,661,368 and 5,719,486 may not be suitable for use as a 42 volt alternator in a vehicle having traditional electrical components as the neutral point 21 volt average output of these alternators may damage the electrical components.
What is needed, therefore, is a vehicle electrical system that can provide a higher voltage (such as 42 volts) from an alternator to a first group of power consumers in a vehicle and that can simultaneously provide a lower voltage from the alternator to a second group of power consumers (such as traditional vehicle electrical components) that cannot tolerate higher voltages.
The foregoing needs are met by a vehicle electrical system for supplying a first load with a first direct current voltage and for supplying a second load with a second direct current voltage lower than the first direct current voltage. The vehicle electrical system includes a multiphase alternating current generator for generating a first alternating current voltage output and a second alternating current voltage output, a first rectifier unit for rectifying the first alternating current voltage output to be supplied to a first energy storage device and the first load, a second rectifier unit for rectifying the second alternating current voltage output to be supplied to a second energy storage device and the second load, and a controller electrically connected to the second rectifier unit for selectively enabling and disabling the second rectifier unit to allow or block current flow from the generator and to the second energy storage device and the second load.
The multiphase alternating current generator has star-connected armature windings with respective phase winding terminations and a common center connection point. The generator generates the first alternating current voltage output at the respective phase winding terminations and the second alternating current voltage output at the common center connection point wherein the average voltage of the first alternating current voltage output is greater than the average voltage of the second alternating current voltage output. The first rectifier unit is electrically connected between the respective phase winding terminations and the first energy storage device and the first load for full-wave rectifying the first alternating current voltage output to be supplied to the first energy storage device and the first load. The second rectifier unit is electrically connected in a circuit path between the common center connection point and the second energy storage device and the second load for rectifying the second alternating current voltage output to be supplied to the second energy storage device and the second load. The controller is electrically connected to the second rectifier unit, the second energy storage device and the common center connection point, and is operable to sense a voltage output level of the second alternating current voltage output and to selectively enable and disable the second rectifier unit to allow or block current flow through the circuit path between the common center connection point and the second energy storage device and the second load in response to the sensed voltage output level.
It is therefore an advantage of the present invention to provide a vehicle electrical system that can provide a higher voltage from an alternator to a first group of power consumers in the vehicle and that can simultaneously provide a lower voltage from the alternator to a second group of power consumers in the vehicle.
It is another advantage of the present invention to provide a vehicle electrical system that can provide a higher voltage (such as 42 volts) from an alternator to power consumers in a vehicle and that can simultaneously provide a lower voltage from the alternator to a second group of power consumers such as traditional vehicle electrical components that cannot tolerate higher voltages.
It is still another advantage of the present invention to provide a vehicle electrical system that can use and control a higher voltage obtained from the phase terminations of the star-connected armature windings of a multi-phase generator and that can use and control a lower voltage obtained from a common center connection point of the star-connected armature windings of the multiphase generator.